Although I seldom post on Five Doves, since I am an elder and a minister in the body of Christ with both knowledge and experience in this area, I will try to answer your question. I'm sure others will also encourage and enlighten you on this subject, with many varied testimonies, each one quite unique. Since God works with each one of us individually without trying to press us all into the same mold there is no "got to do it this way" correct answer.
Just as the most important thing in life is to make sure you are born again, the most important thing about speaking in tongues is to make sure you have received the Holy Spirit. Although frequently a person will speak in tongues when they receive the Holy Spirit, it is not mandatory. It can always come later, but it is very important that you know the supernatural presence of the Spirit of God has taken up his abode in you body. Since he brings supernatural gifts with him when you receive him, there should be a definite awareness that the presence of God has filled his tabernacle by manifesting his presence in you in a powerful way. I say all that because some well meaning ministers encourage candidates to speak in tongues so strongly that they may wind up imitating what they hear without actually receiving the Holy Spirit. If you can't nail down the fact that you knowingly received the Holy Spirit, then forget about tongues for now and go find a church that can help you receive the Holy Spirit.
Assuming that you have been baptized in the Holy Spirit, then let me share some things that will hopefully help you. There is both speaking in tongues, praying in tongues, and singing in tongues, each with its own purpose, but they aren't learned like Jesus' disciples wanted to learn how to pray. Since they are supernatural manifestations of the Holy Spirit, your only part is to yield and cooperate with him, providing him the vehicle to use. What you probably want to learn is how to fully yield to the Holy Spirit so that you aren't constraining him from the full manifestation of his utterance gifts. My advice here is to pray long, pray hard (earnest), and pray often. As you reach the end of your understanding, if he's in you, he will begin to pray through you without you "learning" or "trying" to do anything.
As I go back and read over you questions and statements again, I must recommend that you go find some spirit filled Christians that can help pray with you and answer your questions. You also need to be part of a spirit filled church which can provide the support you need. Since an individual can imitate tongues to some degree, speaking in tongues does not let you know for sure that you have been baptized in the Holy Spirit. This might just be a point of semantics, but we do not attempt to speak in tongues while praying. Speaking in tongues is equated with the simple gift of prophesy which is for the purpose of edification, exhortation, and comfort. When done in the presence of the congregation, it should always be interpreted so everyone will know what the Holy Spirit has said. When we pray, we can choose to pray in tongues in which case, the Holy Spirit intercedes through us for things that we don't know how to pray about. Many times as I pray in my understanding, I will catch myself praying in tongues, not even aware of the point that the spirit began to pray through me. I can choose to deliberately pray in tongues, just like I can choose to speak in tongues but they are different manifestations of the Holy Spirit. I can also choose to sing in the spirit, and sometimes when I am praying in the spirit, the Holy Spirit will complete the intercession and go from praying to singing in the spirit.
Are these things learned, as far as how it's done? No! It wouldn't be a manifestation of the Holy Spirit if it could be learned. I control when I open my mouth, I control how much air I expel (loud or soft), but I don't control the syllables. I hear them through my ears when they are spoken at the same time anyone else would hear them. I don't control my lips and tongue either, and the freer that I can be in yielding my lips and tongue to the Holy Spirit, the fuller of a language that he manifests. On a side note, my wife said that it had to be the Holy Ghost creating the syllables on her vocal cords because she couldn't speak that fast!
According to the Bible, on the day of Pentecost, they began to speak with other tongues, as the Spirit gave them utterance. (Acts 2:4) Notice that they did the speaking, which means that they had to open their mouths and expel air. He used their vocal cords, tongue, and lips to form the utterance, so it is a cooperative process. Very few people are just knocked down and come to themselves speaking in tongues when they are baptized in the Holy Spirit. (As another side note, it did happen to my son-in-law that way.) If possible, we would all want it that way so we could make sure it wasn't just us, but the baptism of the Holy Spirit is also by faith so there is a release of our faith in opening our mouth and allowing him to fill it when we receive him.
As far as how tongues sound, there is no particular way that they must sound, but a spirit filled person can usually tell by the anointing whether the Holy Spirit is the author of a tongue or not. I am reminded of the testimony of one particular person who was bothered that he made popping and clicking sounds when speaking in tongues until an Xhosa native wanted to know how he knew his language. The tongue may be unknown to the person doing the speaking, but the Holy Spirit sometimes speaks in languages known to others as a sign to them.
I could share many scriptures, and my testimony along with many others, but that can't replace personal fellowship with other spirit filled believers. At least you are on the right track and as long as you don't get discouraged, God will not only answer your questions but allow you to experience many supernatural things in due time. Since this letter is already long, I'll do another post on a vision that provides additional insight into the development of a heavenly language.